The effects of proteins on the proton N.M.R. transverse relaxation times of water

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Abstract
The major features of N.M.R. transverse water proton relaxation in solutions of native bovine serum albumin can be quantitatively interpreted in terms of fast chemical exchange between water and protein protons. Transverse proton relaxation dispersions are observed as a function of CPMG pulse spacing and spectrometer frequency and are shown to be consistent with the fast exchange of water with NH and OH protons of the amino acid side chains in the protein. The mean first order exchange rate is about 5 × 103 s-1. Although there is evidence that proteins influence the state of the water around them (the so called ‘bound’ water concept) the results obtained suggest that this influences the proton relaxation in a minor way compared to the potent effect of the chemical exchange mechanism.